Dual/Redundant Self Check Ultraviolet Flame Sensor and Combustion Safeguard Control

ABSTRACT

Two UV tubes are contained in one ultraviolet sensor to monitor one burner flame. Each UV tube is powered during a different time cycle to eliminate interference between the two UV tubes. This is made possible by two rectifier circuits being powered by two transformers that are 180° out of phase with each other. Self check is accomplished by the redundancy of two amplifiers providing output to two flame relays so that if one UV tube was to fail in the conducting mode, the combustion safeguard control will continue to safely monitor the flame by powering the fuel valve when the flame is present and removing power to the fuel valve when the flame goes out.

BACKGROUND OF THE INVENTION

Industrial burners utilize a flame sensor with a combustion safeguardcontrol to enable opening of the fuel valve(s) in the presence of aflame or conversely, to close the fuel valve(s) in the absence of aflame. The preferred optical flame detector is an ultraviolet sensitive,cold cathode, gas discharge tube, hereinafter generally referred to as aUV tube. When ultraviolet rays from a flame are incident upon the UVtube and sufficient voltage potential exists across the electrodes inthe tube, the UV tube conducts. This current is an input to a combustionsafeguard control, which amplifies this input and provides an output tothe fuel valve(s). It is possible for a UV tube to fail in theconduction mode with no UV present. Self check UV tube sensors withmechanical shutters that intermittently shield the UV tube from theflame to identify a failed UV tube are subject to mechanical failure dueto wear and temperature degradation on the moving parts.

BRIEF DESCRIPTION OF THE SEVERAL DRAWING VIEWS

FIG. 1 is a series of diagrams illustrating voltage waveforms;

FIG. 2 is a wiring diagram illustrating the interconnection of thedual/redundant self check ultraviolet sensor, the combustion safeguardcontrol with transformer 180° phase differential, and burner fuelvalve(s).

DESCRIPTION OF THE INVENTION

The purpose of this invention is to include two UV tubes in oneultraviolet sensor to monitor one burner flame. Since UV tubes produceUV rays when they conduct, two UV tubes in one sensor would not normallybe suitable for sensing a burner flame, as one UV tube could beresponding to the other tube and not the flame.

The Dual/Redundant self check ultraviolet flame sensor and combustionsafeguard control features voltage supply to the UV tubes that are outof phase with each other. When one UV tube is powered and may respond toUV rays, the other UV tube is off. The two UV tubes are powered thru tworectifier circuits from two transformers that are out of phase with eachother. The two UV tubes are powered and sense UV from the flame onalternating half cycles (See FIG. 1.) Each UV tube and rectifier circuitprovides input to its own amplifier. Each amplifier provides input toits own flame relay (See FIG. 2.) Upon burner startup, before burnerignition, if either UV tube is in conduction, the safe start checkcircuit does not permit powering the fuel valve.

During the burner run cycle, if either UV tube fails in a conductionstate, the cycle will safely continue with the other UV tube sensing theburner flame.

1. In a burner fuel valve control, a control circuit consists of two UVtubes in one sensor housing, the rectifier circuits, two transformers180° out of phase with each other, two amplifiers, two flame relays(output from amplifier), a safe start circuit and an output circuitcontrolling said burner fuel valve in response to combined circuit. 2.The control circuit of claim 1 wherein output circuit opens fuel valvein response to said presence of UV rays.
 3. The control circuit of claim1 wherein output circuit closes fuel valve in response to said absenceof UV rays.
 4. The control circuit of claim 1 wherein output circuitcloses fuel valve in response to said absence of UV rays even if a UVtube fails in a conducting mode.